Does [itex]-Gm\rho2\pi\left(R_2^2-R_1^2\right)[/itex] make sense for the potential of a point-mass "m" inside a spherical shell of radii [itex]R_1< R_2[/itex] and density [itex]\rho[/itex]? Now I've already found the potential outside of a homogeneous sphere of same density. I'm now asked to use these two results to find the potential inside a homogeneous sphere of again indeity density sphere, using the previous two results. Can I do this by considering the point on the inside of the shell with a sphere in the space in the middle? Does it make sense to add the two potential formulas using the correct radii?